I am going to install my CJM fuel return system very soon along with 440cc injectors and probably the UTEC and I am wondering what I should set the fuel pressure to. It seems that alot of people leave it at 43psi while others are going up to 58psi (per the APS kit). I am told that with 440cc injectors and 58psi, the system will support 450hp without going 100% duty cycle.

I am looking to get to around 400rwhp (or so ) but the motor is not built so I dont want to push it for much more than that yet. So I am wondering if it is worth setting the fuel pressure somewhere in between 43 and 58 (like 50psi maybe)?

Also, are there benefits to staying with a lower fuel pressure?

 

One benefit of staying at a lower base fuel pressure with a return system is warm starts are not an issue.. The higher the pressure the more of a problem re-starting the car while already warm..

Maybe someone else can chime in too but I was told that raising the base fuel pressure won't really make that much of a difference on how much fuel the injectors get at WOT..

--mike

 

I had mine at 52psi [ with vacuum hose hooked up ]. I kept getting the p300 code . I then set it at 52 with out the vacuum hose , and I still get hard starting and the p300 . Im going to try settiing it 48psi and see if that helps with hard starting . I did notice after I reset it with out the hose hooked up . My A/F was higher and I needed to retune it

oh...and yes the hard starting is when the car is warm

 

here is a good thread too:
https://my350z.com/forum/forced-induction/136681-does-voltage-affect-fuel-pressure.html

especially post #10

 

I'd expect it to effect the tunability more than anything else. :unsure:

 

depending on boost, 50 psi with the vacuum not connected to the fpr is the best balance. better to not try to fool the injectors with more pressure, but just get bigger injectors.
i have found the idle portion of the a/f map needs to be pretty conservative in order to get a nice factory start in both cold and hot conditions. i changed my maps tonight, and had a bi t ch of a time starting it when warm. will be switching back in the morn.

 

Turbonetics sets the fuel pressure at 53 PSI out of box...

 

That is now without a fuel return and assuming everything was done right. Of course I have no way to know if I am actually at 52 now but it doesnt really matter. Once the fuel system is installed I need to set the FPR (with vacuum). So I'm wondering what to set it to. Is 48-50 with vacuum reasonable or should I go to 53psi ?

 

53 should be fine....and it give you a good medium between 46 (stock) and 58 (others)

 

Shoot for about 52psi with vaccum line disconnected...this works out to about 44-45psi with the vaccum line attached.

And whoever told you that raising the fuel pressure has no bearing on how much fuel the injectors spray at WOT is 100% wrong. Fuel pressure is critical in tuning...which is why you want a constant differential pressure...ie...by using a 1:1 FPR. Higher fuel pressure will result in more fuel at every single duty cycle.

Everyone is correct, in that the car tends to start better when warm (one blip of the throttle gets the engine started immediately), with less fuel pressure. If you just need 400whp, you run as low as 35psi of fuel pressure, and still have plenty of fuel for tuning purposes.

 

Thanks.
So right now without a rising rate FPR, I am getting more or less 52psi regardless of how much boost. Then with the FPR I will get a 1:1 rise in fuel pressure with each psi of boost. So if I set the initial PSI to around 44 (with vac) and go to 8-9psi I end up in the same ballpark theoretically. I assume that is the logic here.
With the Aeromotive FPR is it just a turn of a screw to adjust the pressure?

 

I am with Shariff, 52ish base pressure is good... it wouldnt bother me if you went a couple more. I have never had a problem running cars at these fuel pressure levels. That means under boost the car will hit 60-64psi depending on how much boost your running, and thats not really considered really high.

One thing that can throw you off is that people are not always clear about how they are setting their fuel pressure. I always use the term "Base Pressure", and that is defined as your differential pressure (the pressure that your at with no vacuum line connected). If you dont have a 1:1 regulator (a regulator with a vacuum line), then your idle pressure will be the same as your base pressure, you will always have the same pressure until your fuel pump cant keep up anymore. If you have a 1:1 regulator, then your idle pressure will be lower then your base pressure, at 0 boost, 0 vacuum your fuel pressure will be the same as your base pressure, and at 10psi of boost your fuel pressure will be your base pressure plus 10 psi. Most of you know this, but I just wanted to throw it in cause not everyone is always clear in how they speak of their fuel pressure.

 

Yup! To adjust the pressure, loosen that nut on top, then turn the allen bolt clockwise to increase or counter-clockwise to decrease the fuel pressure.

 

Actually, without a rising rate FPR, you are getting LESS fuel pressure as the boost rises. Remember that differential fuel pressure is the only pressure people should talking about. This is the pressure coming out of the injector nozzle...after taking into effect that you have X psi pushing back on the injector.

So if you are running 52psi of fuel pressure WITHOUT a rising rate FPR, and you run 10psi of boost, you are only delivering 42psi of fuel through the injector (52psi minus the 10psi of manifold pressure), and into the intake track. With the riser, you will have 62psi of pressure in the line, but the perfect 52psi coming out of the injector.

Hope that makes sense.

 

Gotcha.

If the fuel pressure is set higher and the injector is therefore pumping out more fuel, does that mean you would tune it to a shorter duty cycle?

 

the injector will flow more at the same duty cycle if you increase fuel pressure, so yes it will reduce duty cycle if you increase fuel pressure and tune.